The RAF and US Air Force are primed to support the ground attack with air strikes.

But under the agreement – allegedly brokered by Saudi Arabia – the US-led coalition will only bomb targets agreed with the militants in advance.

AFP

APPROACH: Pro-government forces in Salaheddin province, Iraq

AFP

UNDER ARMOUR: Iraqi forces in Anbar province after clearing the area of ISIS

REUTERS

READY: Iraqi troops prepare to retake Mosul

Iraqi forces launch operation to recapture Fallujah

A major operation to liberate the city of Fallujah, Iraq as battle against Daesh escalates.

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AFP/Getty Images

Iraqi Shiite fighters from the Popular Mobilisation units, monitor the frontline near the Tharthar lake, north of the city of Fallujah

The military source in Moscow said: "In preparation for the operation in Mosul, US intelligence agencies and Saudi Arabia agreed that before the assault all militants will be offered a safe route to leave the city with their families.

“And at the time of the assault, coalition aircraft would only strike empty buildings, agreed in advance with the militants.

"More than 9,000 ISIS fighters will be transferred to the eastern regions of Syria to follow a major offensive operation, which involves the capture of Deir ez-Zur and Palmyra.”